1. Technical Field
The present disclosure relates to a ceramic core, a manufacturing method for the same, a manufacturing method for a casting using the ceramic core, and a casting manufactured by the manufacturing method.
2. Related Art
It has been known that the ceramic core is used for manufacturing a hollow casting. As the hollow casting, a blade for a gas turbine (turbine blade) formed of Ni-based heat-resistant alloy, for example, has been known. This blade has a hollow cooling hole on the inside. This hollow cooling hole may have the complicated and precise structure for increasing the cooling effect. Such a blade can be manufactured using a ceramic core with the shape corresponding to the hollow cooling hole to be formed by the lost wax precision casting method or the like. For example, FIG. 1 illustrates the ceramic core having a blade portion 1 and a dovetail 2 for forming the hollow turbine blade.
A known example of such a ceramic core is one (JP-A-01-245941) including 60 to 85 mass % of fused silica, 15 to 35 mass % of zircon, and 1 to 5 mass % of cristobalite is known. Moreover, a ceramic core (specification of EP Patent No. 0179649) including 60 to 80 mass % of fused silica powder, up to 15 mass % of yttria, and up to 0.2 mass % of alkali metal. As another example, furthermore, there is known a ceramic core (specification of U.S. Pat. No. 4,093,017) formed using fused silica and colloidal silica stabilized with sodium.
In JP-A-01-245941, for example, there are the following descriptions: the ceramic core still has the sufficient mechanical strength at a casting temperature of approximately 1500° C.; since the remarkable change in dimension of the ceramic core during the casting is suppressed, the ceramic core exhibits the excellent dimension stability; and after the casting, this ceramic core is easily eluted from the casting. The specification of EP Patent No. 0179649 describes that the ceramic core has a room-temperature strength of 12 MPa at maximum and has the property of substantially retaining its shape even at a temperature of 1675° C., which is much higher than 1500° C. Furthermore, the specification of U.S. Pat. No. 4,093,017 describes that the ceramic core has a room-temperature strength of approximately 7 MPa.